01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Autoimmune pancreatitis is an immune-mediated pancreatic disease that can resemble malignancy and can often respond to immunosuppressive treatment. It is not one uniform diagnosis. Type 1 belongs to the wider spectrum of IgG4-related disease, whereas type 2 has different histological and clinical associations. Identifying the subtype influences the search for other-organ disease, interpretation of serology and assessment of relapse risk. The initial responsibility is to assemble a coherent diagnosis without using steroid responsiveness as a shortcut around pancreatic cancer.
Treatment aims to relieve symptoms, reverse active inflammation where possible and protect organ function while limiting toxicity. A patient may have pancreatic enlargement, bile-duct involvement, impaired glucose control and nutritional consequences at the same time. Remission requires objective reassessment rather than a report of feeling better alone. The steroid schedule must be tied to a defined clinical protocol and exact product, because published regional regimens differ and both disease relapse and adrenal suppression influence the subsequent taper.
Key points
- Type 1 autoimmune pancreatitis is the pancreatic manifestation of IgG4-related disease and can involve bile ducts, salivary glands, kidneys and other organs.
- Type 2 is a distinct duct-centred disorder with granulocytic epithelial lesions; inflammatory bowel disease is an association and serum IgG4 may be normal.
- Combine imaging, tissue, serology and other-organ assessment. Neither a raised IgG4 nor a small negative biopsy settles the diagnosis; complete the malignancy assessment before a steroid trial, whose response does not itself exclude cancer.
- A steroid response does not exclude cancer. A specialist assessment for malignancy precedes any diagnostic steroid trial.
- Treat symptomatic or organ-threatening confirmed disease with a specialist plan; do not prescribe steroids simply because IgG4 is mildly elevated.
- An illustrative selected regimen is oral prednisolone 0.6 mg/kg/day for four weeks, with clinical, biochemical and imaging response assessed at two to four weeks.
- Taper according to the selected protocol, disease activity and adrenal risk; after prolonged treatment do not stop abruptly, and slow withdrawal near 7.5 mg/day.
- Follow pancreatic function and extra-pancreatic disease long term; maintenance treatment is individual and type 1 has a greater relapse tendency than type 2.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Type 1 IgG4-related inflammation
Type 1 autoimmune pancreatitis belongs to a systemic fibro-inflammatory disorder that can affect multiple organs. Pancreatic disease may appear alongside biliary, salivary, renal or retroperitoneal involvement, shaping the diagnostic assessment and follow-up.
Type 2 duct-centred disease
Type 2 autoimmune pancreatitis is a distinct inflammatory process centred on pancreatic ducts. It can be associated with inflammatory bowel disease and generally lacks the characteristic systemic IgG4-related pattern of type 1.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Lymphoplasmacytic and fibrotic injury
Type 1 disease combines lymphoplasmacytic inflammation, storiform fibrosis, obliterative phlebitis and increased IgG4-positive plasma cells in a characteristic tissue pattern. No single component should be interpreted independently of morphology and the clinical setting.
- 2Granulocytic epithelial lesions
Type 2 disease shows neutrophilic injury to duct epithelium, producing the characteristic granulocytic epithelial lesion. This explains why its diagnosis depends heavily on suitable tissue and cannot be established through the type 1 serological pattern.
- 3Inflammation versus established damage
Active immune inflammation may improve with treatment, while fibrosis and lost pancreatic function may persist. This distinction explains the need to assess both remission and longer-term digestive or endocrine consequences after the acute treatment response.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Painless or mildly painful obstructive jaundice, pancreatic enlargement and worsening glucose control may lead to diagnosis. Look for salivary or lacrimal swelling, renal involvement, retroperitoneal disease and biliary strictures. These findings support a systemic pattern but do not eliminate the possibility of malignancy; explain which organs need assessment and how the findings fit together.
Type 2 disease can present like acute pancreatitis, often in a younger patient, and may be associated with inflammatory bowel disease. It is not simply type 1 disease with a normal blood test. Its characteristic duct-centred neutrophilic injury and granulocytic epithelial lesions require appropriate pathological interpretation, while the typical systemic IgG4 pattern is absent.
Determine whether symptoms or threatened organ function justify treatment, and establish glucose control, infection risk, blood pressure, fluid status, bone health, psychiatric history and current medicines before steroids. An asymptomatic biochemical abnormality alone is not equivalent to organ-threatening inflammation. Balance the need for prompt disease control against hazards that require treatment or monitoring first.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Pancreatic CT or MRI/MRCPFirst step - Why
- Assess the parenchymal and ductal pattern and evaluate a possible malignancy.
- Interpretation and limitations
- Diffuse enlargement, a capsule-like rim and long duct narrowing without marked upstream dilatation support autoimmune pancreatitis, but focal disease can closely mimic cancer. Review imaging with specialist radiology and correlate it with tissue and serology. A suggestive pattern does not make every invasive investigation unnecessary or establish the subtype by itself.
- 02
IgG4 and other laboratory findings - Why
- Support assessment of type 1 disease and identify biochemical consequences.
- Interpretation and limitations
- Measure serum IgG4 when the disease is suspected, but remember that it may be normal in type 1 and is commonly unhelpful in type 2. Elevated levels also occur in other diseases, including malignancy. Liver tests, glucose and appropriate nutritional assessment identify organ effects. CA19-9 is also non-specific, especially with cholestasis, and cannot independently distinguish cancer from inflammation.
- 03
EUS-guided tissue with pathological review - Why
- Obtain material that addresses both malignancy and autoimmune histology.
- Interpretation and limitations
- Core tissue can preserve the architecture needed to identify lymphoplasmacytic inflammation, storiform fibrosis, obliterative phlebitis and IgG4-positive cells in type 1, or granulocytic epithelial lesions in type 2. A negative or non-specific small sample may reflect sampling error. Persistent cancer concern requires renewed multidisciplinary assessment rather than an automatic steroid trial.
- 04
Baseline and response assessment - Why
- Document disease activity and treatment safety before and during induction.
- Interpretation and limitations
- Record the relevant symptoms, examination, liver profile, glucose, renal function, blood pressure and baseline imaging. At two to four weeks assess clinical, biochemical and morphological response together. Poor response or progression requires reconsideration of the diagnosis, including infection and malignancy; serum IgG4 alone is insufficient to establish remission or relapse.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Pancreatic and biliary malignancy
Focal enlargement, obstruction and weight loss overlap with cancer. Mild IgG4 elevation and non-specific inflammatory biopsy findings do not reliably separate the conditions, and persistent diagnostic discordance warrants further specialist investigation.
Other forms of pancreatitis
Acute or chronic pancreatic injury from stones, exposures, metabolic causes or duct disease can overlap clinically and radiologically. Autoimmune features need positive assessment rather than being assigned after a limited initial work-up is negative.
Other inflammatory or infiltrative disease
Primary sclerosing cholangitis, lymphoma and other systemic processes can resemble elements of IgG4-related disease. Organ distribution, representative pathology and clinical evolution help distinguish these conditions and avoid inappropriate immunosuppression.
Additional chapter-specific clues
A focal mass, jaundice and weight loss can occur in either autoimmune disease or cancer. Mild IgG4 elevation and non-specific inflammatory cells are insufficient reassurance. Assess the whole imaging and pathological picture in the pancreatic multidisciplinary team; a discordant or inadequately sampled lesion may require repeat investigation before treatment is safe.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked caseTreating confirmed type 1 disease safelyFirst stepA 50 kg adult develops jaundice and mild upper abdominal discomfort. Imaging shows diffuse pancreatic enlargement and bile-duct involvement without features of cholangitis.+
- 1The pancreatic team reviews imaging, markedly elevated IgG4 and a representative core biopsy showing the characteristic type 1 pattern. The complete assessment is concordant and important malignant alternatives have been addressed; the absence of malignant cells is not used in isolation. After infection, glucose, bone and medicine review, the team prescribes Milpharm prednisolone 5 mg soluble tablets, six tablets (30 mg) orally each morning for a planned four-week induction, with written safety and taper instructions.
- 2At two weeks the jaundice and discomfort have improved, bilirubin has fallen from 108 to 34 micromol/L and repeat imaging shows reduced pancreatic and biliary inflammation. Glucose and blood pressure remain acceptable and there are no significant psychological or infectious adverse effects. The team continues the induction to the planned four-week review rather than stopping on the strength of early symptom relief.
- 3At that review, objective improvement is sustained and the specialist starts the agreed gradual taper, initially reducing by 5 mg every two weeks while reassessing disease activity. The plan requires slower reductions around 7.5 mg and below according to adrenal and relapse risk. The patient carries steroid treatment information, has instructions for intercurrent illness and cannot-retain-tablets symptoms, and has long-term pancreatic and other-organ follow-up arranged.
02Establish the diagnosisAutoimmune pancreatitis is a possibilityThe patient has a pancreatic abnormality or an IgG4-related pattern that needs explanation.+
- 1Characterise pancreatic and biliary imaging, serology, symptoms and relevant other-organ findings. Use representative tissue when the diagnosis or exclusion of cancer requires it. Distinguish the type 1 systemic pattern from type 2 duct-centred disease; do not use a serum IgG4 result to classify every patient.
- 2If a focal lesion or other finding remains concerning, discuss further tissue, imaging or surgical assessment before steroids. A carefully supervised diagnostic trial is reserved for an appropriate specialist setting after a negative malignancy work-up. Even an apparent response does not prove that cancer is absent, so unexpected persistence or recurrence needs reassessment.
- 3Agree whether active symptoms or a threat to organ function warrants treatment. Deal urgently with cholangitis or another infection when present; biliary drainage is a separate anatomical decision and is not automatically required for every stable jaundiced patient with confirmed disease. Coordinate the pancreatic, biliary and systemic aspects through the responsible team.
03Induce remission and plan beyond itTreatment has been selected after diagnostic assessmentThe patient has symptomatic autoimmune disease and the treatment risks have been reviewed.+
- 1Use a specified induction protocol and product. JPS guidance explicitly supports oral prednisolone 0.6 mg/kg/day for two to four weeks; the European digestive guideline describes 0.6–0.8 mg/kg/day prednisone-equivalent treatment for a month. The 30 mg four-week example for a 50 kg adult is a selected specialist regimen, not a dose for an undiagnosed pancreatic mass or every IgG4 elevation.
- 2Assess response at two to four weeks and taper with repeated clinical review. Published schedules differ: the detailed European digestive recommendation gives 5 mg reductions every two weeks over a three-to-six-month taper, while the French November 2025 systemic PNDS uses prednisone 0.4–0.6 mg/kg/day for three to four weeks and an individual taper generally over three months. Keep those population and drug distinctions; no single agreed taper applies to every patient.
- 3If response is poor, revisit the diagnosis and possible infection or malignancy before reflexively increasing immunosuppression. After remission, assess the need for maintenance from relapse history, organ involvement and treatment toxicity. Specialist steroid-sparing treatment may be appropriate in recurrent or resistant disease; long-term steroids are not automatic for all type 1 patients and are generally less often needed in type 2.
Key medicines and prescribing safety1 treatment · regimens, roles and cautions+
Milpharm prednisolone 5 mg soluble tablets
Selected specialist off-label adult AIP induction: 0.6 mg/kg orally once daily in the morning for a planned four weeks; a 50 kg adult receives 30 mg (six 5 mg tablets). Dissolve in water, or swallow the tablets whole. Review clinical, biochemical and imaging response at two to four weeks. If remission permits, an initial taper of 5 mg every two weeks is one protocol-based approach; slow reductions around 7.5 mg/day and below, guided by disease activity and adrenal recovery. Do not stop abruptly after this course.Do not use with product hypersensitivity or untreated systemic infection; specific anti-infective treatment is required when infection is present. Avoid live-virus immunisation during immunosuppression. Give steroid treatment information and instructions for illness, surgery or inability to retain tablets; prolonged therapy can suppress the adrenal axis. Monitor glucose, BP, fluid status, potassium, infection, mood, eyes and bone risk. Renal impairment/HF increases fluid-retention concern; liver failure can increase exposure and needs closer monitoring, with no fixed adjustment table. Use particular care with older age, diabetes, osteoporosis, peptic ulcer, glaucoma, severe affective illness, recent MI, TB or systemic sclerosis; the latter carries renal-crisis risk, so monitor BP and renal function. Seek urgent advice for chickenpox/shingles or measles exposure, serious infection, severe mood or suicidal symptoms; do not independently stop established steroids. Refer new visual disturbance for assessment. Avoid strong CYP3A-inhibitor combinations unless benefit justifies risk; enzyme inducers may reduce effect. Review NSAIDs/aspirin for GI bleeding, monitor INR with warfarin and potassium with potassium-lowering drugs; methotrexate may increase blood toxicity. Pregnancy requires a benefit–risk decision. Up to 40 mg/day during breastfeeding is unlikely to cause systemic infant effects; higher doses need review. Store below 30°C protected from light.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Obstruction and organ dysfunction
Pancreatic or biliary inflammation can cause jaundice, while renal or other extra-pancreatic involvement may threaten organ function. These effects determine treatment urgency and may require supportive or anatomical intervention alongside immune treatment.
Relapse and functional loss
Type 1 disease has a greater tendency to relapse than type 2, sometimes in a different organ. Exocrine insufficiency, diabetes and nutritional or skeletal consequences may persist despite an initially good steroid response.
Immunosuppressive treatment toxicity
Steroid treatment can worsen glucose control, infection risk, bone health, mental state and fluid retention, and can suppress adrenal function. A safe course includes monitoring, patient education and an individualized withdrawal plan.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- During induction, compare the same clinical and organ-specific biochemical findings with baseline, and obtain planned morphological reassessment at two to four weeks. Failure to improve needs a diagnostic review, not just a higher dose based on an isolated IgG4 result.
- Review glucose, blood pressure, fluid balance, infection, sleep and mental state early, especially in a patient with pre-existing risks. Assess bone protection and visual symptoms during continuing therapy; make the responsible service and contact route clear to the patient.
- During tapering, distinguish disease recurrence from steroid withdrawal or adrenal insufficiency. New jaundice, pancreatic symptoms or other-organ dysfunction requires objective assessment. A rise in IgG4 can contribute information but should not independently dictate indefinite high-dose treatment.
- Provide long-term follow-up for type 1 disease, including exocrine and endocrine function, nutrition and affected extra-pancreatic organs. Review maintenance need and toxicity individually. A new focal lesion or unexplained deterioration retains a cancer differential even after a previous convincing autoimmune diagnosis.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Histology needs architecture and context
IgG4-positive cells can occur around a tumour and are not sufficient alone to establish autoimmune disease. Preserved core architecture helps identify the characteristic pattern, but sampling error remains possible. Explain what the specimen demonstrates and what uncertainty remains rather than treating a negative cytology report as definitive reassurance.
Type 2 is a separate disorder
Granulocytic epithelial lesions and an association with inflammatory bowel disease distinguish type 2 from the systemic IgG4-related form. Normal serum IgG4 is therefore expected in many type 2 presentations and should not be used to exclude all autoimmune pancreatitis. Tissue and clinical context remain central.
Response is evidence, not a cancer exclusion test
Steroids can change inflammatory findings without resolving every diagnostic uncertainty. A specialist trial is interpretable only within a completed baseline assessment and objective follow-up. A focal lesion that persists or behaves unexpectedly deserves renewed investigation, even if some symptoms or laboratory results improve.
Regional schedules must not be blended
European digestive, Japanese pancreatic and French systemic guidance differ in their induction ranges, taper and maintenance practices. Select and document the appropriate protocol with the specialist team. The exact drug and product still need their own safety checks, particularly when withdrawal approaches physiological steroid exposure.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling a mildly raised IgG4 diagnostic of type 1 autoimmune pancreatitis or using a normal IgG4 to exclude type 2 disease.
- 02
Starting an empirical steroid trial for an unresolved pancreatic mass before an appropriate cancer and infection assessment.
- 03
Treating a small negative or non-specific biopsy as absolute exclusion of malignancy despite discordant clinical or imaging findings.
- 04
Stopping a four-week steroid induction abruptly because jaundice has improved, without considering relapse and adrenal suppression.
- 05
Using serum IgG4 alone to define treatment success, or assuming that every patient needs indefinite maintenance steroids.